With the development and wide application of LED illumination, LED phase cut dimming power supply is more and more widely used since it is convenient for user's installation and wire arrangement. However, at present, most of LED phase cut dimming power supplies applied produce the dimming effect by reducing the output power through the adjustment of the input to restrict the power. Such a method has a certain restriction on the load power. When the load power is lower than a certain range, the dimming effect will become poorer, and there would be poor compatibility with the phase cut dimmer, narrow dimming range and other shortcomings. Some adopt the output pulse width (PWM) dimming control circuit. However, the primary sampling signal of LED phase cut dimming power supply is transmitted to the secondary directly through the optocoupler, and then the signal is converted into a pulse width (PWM) with a single-chip microcomputer to control the output voltage pulse width of LED phase cut dimming, power supply. Although this method does not restrict the load power, great temperature drift of the optocoupler will result in signal voltage distortion, and the output voltage pulse width of LED phase cut dimming power supply will be affected. In addition, since the single-chip microcomputer is adopted, the levels of output pulse width (PWM) dimming is generally divided into 256 ones, and the dimming elect changes in steps. So, the gentleness of the dimming effect is not good enough.
To sum up, in the existing technologies, LED phase cut dimming power supply has restriction on load power, poor compatibility with the phase cut dimmer, narrow dimming range, great temperature drift, poor dimming effect and other defects.